The present invention relates to a method for determining the operating conditions in a continuous metal casting machine of the type having an endless casting belt for confining molten metal introduced into the input of the machine, and more particularly to a method for determining the pool level of the molten metal supplied to the input region of the belt casting machine.
Continuous casting machines are used to cast long lengths of metal strip or slab of preselected dimension directly from molten metal. The molten metal is confined adjacent to the front surface of a flexible, endless moving metal belt which is moved along with the metal being cast as the molten metal is introduced into the machine from an external source. The molten metal is carried along by the casting belt as it solidifies, while a high velocity flow of liquid coolant is applied along the reverse surface of the casting belt to cool it and to extract heat from the metal adjacent to the belt, thereby providing solidification of the metal into the strip or slab being formed by the machine.
It is important that the molten metal be introduced into the input region of the continuous casting machine at a rate which is effectively synchronized with the casting rate of the machine as determined by the belt travel to maintain the pool of molten metal in the input region of the machine at a desired level. When the input feed rate exceeds the casting rate, the pool level will creep up. When the input feed rate is less than the casting rate, the pool level will creep down into the machine allowing the molten metal being introduced to cascade too far before reaching the pool causing splashing and turbulence within the machine. Such splashing and turbulence causes non-uniformity and segregation in the cast product.
When the input feed rate is accurately and controllably matched to the casting rate, these casting belt machines can be run continuously for long periods to successfully and efficiently cast large tonnages of strip or slab product. In practice, it is difficult to meter precisely the input feed rate of molten metal and also difficult to determine the level of the molten pool, because in most cases the molten pool is hidden from sight by the equipment associated with the input region of the machine.
The continuous movement of the casting belt and the high velocity liquid coolant rushing along the reverse surface of the belt are further impediments to the determination of pool level. Since the molten metal is at its highest temperature as it is being introduced into the pool, the amount of heat flux is greatest, and so intense and continuous cooling of the reverse surface of the belt is essential in the input and pool region of the casting machine.
A variety of methods have previously been used in attempts to determine the pool level of molten metal being cast in such continuous casting machines. Among these methods is the use of the operator's eye as well as photoelectric and thermal sensors. (Even radioactive sources of neutrons have been suggested for using neutron penetration to sense metal levels.) However, these prior art techniques, including visual observations, have often been less than fully satisfactory.
Improved results have been obtained by the method and apparatus disclosed in U.S. Pat. Nos. 3,364,973; 3,921,697; and 4,712,602. The present invention is directed to improving further the resolution and accuracy of the manner in which pool level is determined by the method and apparatus disclosed in these patents as well as providing redundancy to increase accuracy and reliability.
Furthermore, when casting high temperature melting metals such as steel in thin sections, pool-level sensing is even more difficult, because the input region is narrow in height and blocked from visual observation. This narrow vertical height when casting thin sections means that the entering free stream of molten metal running down into the pool is often some 50% to 70% of the thickness (height) of the mold cavity itself in which the cast product is being formed. A wave or splash of the entering stream or molten metal pool input will produce rapid changes in contact of very hot metal with the casting belt, causing inaccuracies or confusions in pool level determinations. Accordingly, increased resolution and accuracy is very desirable, particularly when casting thin sections of high temperature melting metals, such as steel.